1. Field of the Invention
The present invention relates to an exhaust gas turbine that is driven by exhaust gas emitted from an engine, more specifically, the present invention relates to an exhaust gas turbine equipped with an exhaust gas control valve, i.e. a waste gate valve, for closing and opening an exhaust gas bypass passage so that the exhaust gas emitted from an engine bypasses the exhaust gas turbine and flows into an exhaust gas outlet passage.
2. Background of the Invention
In an exhaust gas turbocharger of a relatively smaller size class, the exhaust gas turbine therein that is driven by the exhaust gas emitted from the engine is provided with a waste gate valve for closing and opening the exhaust gas bypass passage through which the exhaust gas emitted from the engine toward the exhaust gas turbine bypasses the exhaust gas turbine and flows into an exhaust gas (waste gas) outlet passage; in a case where the flow rate of the exhaust gas toward the turbine becomes excessive, the waste gate is relatively opened so that a part of the exhaust gas toward the turbine bypasses the turbine and flows into the exhaust gas outlet passage; and, the flow rate through the turbine is controlled so as to be kept at an pertinent flow rate level. Thus, the engine boost pressure during the higher load side operation is enhanced by relatively closing the waste gate valve that is relatively opened during the lower load side operation where the exhaust gas flow rate is surplus. It is noted that the term “relatively open” or “relatively close” means that the valve is not of an on-off type.
FIGS. 3(A) and 3(B) show the structure of the waste gate valve (the exhaust gas flow rate control valve) as well as the structure around the waste gate valve in the exhaust gas turbine of the exhaust gas turbocharger; FIG. 3(A) shows a longitudinal section as to the drive part of the waste gate valve; FIG. 3(B) shows the A-A cross section in FIG. 3(A).
The exhaust gas turbine 100 shown in FIGS. 3(A) and 3(B) comprises: a turbine casing 1 in which a turbine 2 (detail not shown) is provided; a waste gate valve 3 through which the exhaust gas that is supplied from the engine (not shown) toward the turbine 2 is diverged in an exhaust gas passage 6 to bypass the turbine 2, and flows into an exhaust gas (waste gas) outlet passage 5a, through an exhaust gas bypass passage 5. In addition, the numeral 4 denotes an exhaust gas inlet flange (of the turbine casing 1) by which the waste gate valve is fitted to the engine or a pertinent component relating to the engine.
A valve body 3a of the waste gate valve 3 opens and closes the exhaust gas bypass passage 5 with reciprocating movements or hinge-like movements; in closing the exhaust gas bypass passage 5, the valve body 3a sit on a valve seat 5b that is formed on the outer side surface of the turbine casing 1 around the exhaust gas bypass passage 5; in opening exhaust gas bypass passage 5, the valve body 3a leaves the valve seat 5b so that a part of the exhaust gas (the bypassing exhaust gas) flows from the exhaust gas passage 6 into the exhaust gas (waste gas) outlet passage 5a along the curved arrow direction as depicted in FIG. 3(B).
A support axis (shaft) 8 of an L-shape is fastened to the valve body 3a of the waste gate valve 3, at an end part 8b of the support axis (shaft) 8, by means of a rivet (coupling) 8c. The support axis (shaft) 8 is rotation-freely (swing-freely) fitted in a bush 7 that is fixed to the turbine casing 1 (or, in a guide hole that is provided in the turbine casing 1).
An arm 9 is fixed to a shaft end part of the support axis (shaft) 8, by means of a caulking device 9a or the like. The arm 9 is provided with a connecting part 13 via which the support axis (shaft) 8 is connected to an actuator (not shown) therefor. Thus, according to the swing movements of the connecting part 13, the support axis (shaft) 8 is rotated or swung around an axis 8a thereof; further, via the rotation (rotational swing) movements of the support axis (shaft) 8, the valve body 3a of the waste gate valve sits on or leaves the valve seat 5b, namely the valve body opens or closes the exhaust gas bypass passage 5.
In the patent reference 1 (JP1995-10434), a technology is disclosed regarding a method for firmly locking a swing arm as well as a swing lever of the waste gate valve; whereby, a spring-biased lock lever interlocks the swing lever (and the swing arm) in a manner that a cam surface of the lock lever comes in contact with a cam surface of an end part of the swing lever, and presses the latter cam surface along the contact tangential direction so that the former cam surface interlocks the latter cam surface when the waste gate valve is closed and a control rod is placed at a retired position. Thus, the patent reference 1 provides a technology whereby the valve body of the waste gate valve is firmly fixed to a predetermined valve-closing position.
As shown in FIGS. 3(A) and 3(B), through the waste gate valve 3, the exhaust gas that is supplied from the engine toward the exhaust gas turbine 2 is diverged in the exhaust gas passage 6 which is located upstream of the turbine 2; a part of the exhaust gas before the turbine 2 bypasses the turbine 2, and flows into the exhaust gas (waste gas) outlet passage 5a, through the through an exhaust gas bypass passage 5.
Further, according to the swing movements of the connecting part 13 via which the support axis (shaft) 8 is connected to the actuator therefor, the support axis (shaft) 8 is rotated (swung) around an axis 8a thereof; thus, via the rotation (rotational swing) movements of the support axis (shaft) 8, the valve body 3a of the waste gate valve sits on or leaves the valve seat 5b, namely the valve body opens or closes the exhaust gas bypass passage 5.
The bearing area between the bush 7 and the support axis (shaft) 8 that are exposed to the exhaust gas of high temperature is of an oil free type as it is difficult to provide the bearing area with a lubrication condition; thus, the running surfaces as to the bush 7 and the support axis (shaft) 8 of the waste gate valve 3 is prone to wear down in response to the frequency of use (or the operating hours) thereof.
In addition to the non-lubrication condition, or in response to the trend of the nowadays boost increasing, the levels of the waste gate valve vibration along the X-arrow direction as shown in FIG. 3(B) the vibration which is caused by the engine vibration or the exhaust gas flow pulsation become greater and greater; thus, it becomes a prerequisite to restrain the wear around the bearing area between the bush 7 and the support axis (shaft) 8, in consideration of not only the valve closed condition but also over the whole operating conditions.
As a matter of fact, in the conventional technology of the patent reference 1 (JP1995-10434), the valve body of the waste gate valve is firmly pressed and maintained to a predetermined location in a case where the valve is closed; however, the valve body is not firmly maintained at an expected location in a case where the valve is half-opened. In other words, the vibration reduction effect as to the waste gate valve cannot exceed the desired level, in the case where the valve is half-opened.